Various types of wavemaker devices are known in the prior art. FIGS. 1A-1C illustrate the general concepts of the piston-type, flap-type, or plunger-type wavemakers, respectively, that can generate water waves W of varying amplitude and/or period in a wave tank. In FIG. 1A, piston P action applies a varying force to a vertical wave-board WV, driving it back and forth (indicated by opposite arrows) to generate waves W. In FIG. 1B, piston P action applies force to a pivotable flap wave-board WF to generate waves W. In FIG. 1C, piston P action applies force to a wedge WW, driving it vertically up and down to generate waves W.
The following equations are generally known for comparing the wave height (H) versus stroke length (S0) for first-order piston-type and flap-type wavemakers. The plunger-type equation is not shown as it uses a more involved derivation. Variables in the equations are water depth (h) and wavelength (λ) where (k=2π/λ). These equations are described in Physical Models and Laboratory Techniques in Coastal Engineering by S. A. Hughes (1993), Volume 7, Advanced Series on Ocean Engineering, World Scientific Publishing Co. Pte. Ltd.
First-Order Piston-Type Wavemaker:
      H          S      0        =            4      ⁢                          ⁢      sin      ⁢                          ⁢              h        2            ⁢                          ⁢      kh                      sin        ⁢                                  ⁢        h        ⁢                                  ⁢        2        ⁢        kh            +              2        ⁢        kh            First-Order Flap-Type Wavemaker:
      H          S      0        =                    4        ⁢                                  ⁢        sin        ⁢                                  ⁢        h        ⁢                                  ⁢        kh                              sin          ⁢                                          ⁢          h          ⁢                                          ⁢          2          ⁢          kh                +                  2          ⁢          kh                      ⁢          ⌈                        sin          ⁢                                          ⁢          h          ⁢                                          ⁢          kh                +                              (                          1              -                              cos                ⁢                                                                  ⁢                kh                                      )                    kh                    ⌉      
Driving a wave-board, flap or wedge may be accomplished through a hydraulically driven piston or by a rotary electric motor coupled to a linear actuator that converts rotary action into linear reciprocating motion. Hydraulically driven systems are often more complex requiring an external hydraulic pump. Other wavemakers may generate waves by pneumatic means, such as those described in U.S. Pat. No. 4,467,483 and U.S. Pat. No. 4,812,077 and U.S. Published Application 2009/0038067, or pulsing of water flow, as described in U.S. Pat. No. 5,782,204 for aquariums or reef tanks.
A plunger-type wavemaker using a linkage to a rotary electric motor is described in U.S. Pat. No. 4,507,018 and U.S. Pat. No. 4,705,428. Generating waves with a plunger-type generator using a rotating arm is shown in U.S. Pat. No. 3,973,405. A rotary electric motor used with a flap-type wavemaker is shown in U.S. Pat. No. 2,663,092, and a hydraulically driven flap-type wavemaker is shown in U.S. Pat. No. 4,976,570 and U.S. Pat. No. 4,062,192.
For piston-type rotary electric motor-driven wavemakers, waves may be generated by the movement of a partially submerged vertical wave board, which is linked to a nut that traverses back and forth by means of a motor-driven lead screw or ball screw linear actuator, as shown in U.S. Pat. No. 4,406,162. For a motor-driven ball screw linear actuator, the range of possible wave heights and wave lengths that can be generated for a certain water depth is limited by the distance the wave board can travel (stroke length) as well as its speed of travel. As the length of the ball screw increases (stroke length), ball screws reach a critical speed where the added stroke length can cause the lead screw to oscillate or whip between bearing supports, increasing the risk of lateral buckling. At higher speeds, the operation of the ball screw and gearbox can be noisy. As the screw is often placed over the water tank, lubrication of oil or grease applied to the screw to reduce mechanical wear and tear has the propensity to drip and thereby contaminate the water below.
When the wave board is required to move a greater volume of water at deeper water depths and/or travel at a faster rate of speed, loading of the motor increases. To ensure that the motor speed does not decrease under load, so that the correct wave profile is generated, a position sensor and/or a speed sensor, is often used. For many wavemakers, the sensors are mounted at the end of the motor, which extends the overall length of the wavemaker. As the wave board oscillates back and forth, a loss of position accuracy can result from wavemakers that experience gear lash from either the gearbox and/or from the screw.
Wave absorbers made of foam, expanded metal, etc. are used to dampen waves from the wavemaker. Adaptive control can be implemented to allow the wavemaker to cancel out reflected waves that come in contact with the wave board, which would otherwise interfere and thereby distort the wave profile being generated by the wavemaker. U.S. Pat. No. 4,406,162 describes active control for a wavemaker using a liquid level sensor to control the position of the wave board so that the wavemaker cancels reflective waves. Forced-feedback control can also be used with wavemakers to dampen reflective waves. For less expensive wavemakers that do not have this more complex control, the wavemaker can be shut off before the reflective wave reaches the wave board; otherwise, the wave being generated will be corrupted as it will contain this reflective component.
Removal of a wavemaker from a wave tank may be required when the wave tank is to be used for other purposes, such as experiments involving the circulation of water within the tank, etc. If a wavemaker is not self-supporting due to a complex inter-relationship of mechanical parts of the types previously described, the wavemaker would have to be unbolted and disassembled from the tank to remove it and a separate mounting structure would be required for storing the wavemaker. Removal of hydraulic systems is more involved. The repeated disconnection of hoses increases the likelihood of hydraulic fluid leaks over time. Less complex rotary electric motor-driven wavemakers are often utilized in small wave tanks. Therefore, it would be desirable to have a removable wavemaker whose structure is entirely self-supporting so that it can be removed from and installed on a wave tank easily and conveniently.